The present invention relates to flat panel displays, and more particularly, to improved holographic backlights and liquid crystal display systems employing them.
The assignee of the present invention manufactures holograms for use in holographic lighting devices and in holographic displays, including flat panel displays, and the like. Patents of the assignee of the present invention that are somewhat related to the present invention include those related to trapped beam holographic displays and lighting devices, and include U.S. Pat. No. 5,101,193 entitled "Universal stand-alone Holographic Center High Mounted Stoplight", U.S. Pat. No. 5,347,435 entitled "Linear Lamp Trapped Beam Holographic Center High Mounted Stoplight", and U.S. Pat. No. 5,341,230 entitled "Waveguide Holographic Telltale Display".
Existing color flat panel displays for laptop computers include a backlight, a red/green/blue absorptive filter, and an active matrix liquid crystal display. The backlight includes one or multiple cold cathode fluorescent tubes which inject light into a light pipe that is designed to gradually couple light out over the entire surface of the light pipe. In this manner, it is possible to provide an emitting surface of uniform brightness white light. The white light passes through the red/green/blue absorptive filter and then the active matrix liquid crystal display to create a color image.
However, there are a number of disadvantages of this technology that limits the performance of conventional flat panel displays. A conventional backlight emits nearly randomly polarized light. However, an active matrix liquid crystal display has a linear polarizer at its input side and therefore filters out more than 50% of the randomly polarized light. This results in relatively low transmittance of light from a conventional backlight through the active matrix liquid crystal display.
The light from a conventional backlight is uniformly emitted over the backlight surface, but the active matrix liquid crystal display elements have clear apertures over only about 40% of their surface to make room for electronics. Therefore, a large portion of light emitted from current backlights is wasted because it is blocked by the opaque portions of the active matrix liquid crystal display.
The emitted light from a conventional backlight is uniformly white light over the entire surface of the backlight. However, each of the red/green/blue filters is designed to be transmissive for one color only (red, green, or blue). Therefore, the transmittance of this light through the red/green/blue filter is only 20-30%.
Current backlights emit light over a wide angular field of view. However, the active matrix liquid crystal display works with high contrast only for light that is incident at a near-normal angle relative to the display surface. Therefore, current displays lose contrast rapidly as one moves his or her viewing location away from normal.
Therefore, it is an objective of the present invention to provide for improved holographic backlight liquid crystal display systems employing holographic backlights that overcome the limitations of conventional displays and improved liquid crystal display systems employing the holographic backlights.